Golden State Killer Case: Genetic Material on DNA Website Led Cops to Joseph James DeAngelo: Report

Genetic material shared on an "open-source" genealogy website helped investigators narrow in on the man they say is the Golden State Killer.

After matching crime scene DNA to genetic material from a relative of Joseph James DeAngelo who was registered on a genealogy site, police zeroed in on the 72-year-old ex-cop, who was arrested Tuesday at his Citrus Heights home, the Sacramento District Attorney’s office confirmed first to the Sacramento Bee and The New York Times.

Though DeAngelo’s arrest came just five days after he first became an official suspect, authorities had long been working through online family trees that appeared to match DNA samples from crimes connected to who was then referred to as the East Area Rapist, Chief Deputy District Attorney Steve Grippi told The Bee.

After DeAngelo came into focus, it was learned that he had lived in areas where the attacks occurred and was in the right age range, Grippi said.

DeAngelo was put under surveillance and his DNA was taken from something he discarded, officials said. It came back a match to DNA found at murder scenes in Ventura and Orange counties, authorities said.

But investigators said they wanted to be even more certain, and a second sample was ordered to be tested. It too came back a match, officials said.

"The second sample was astronomical evidence that it was him," Sacramento County District Attorney Anne Marie Schubert told the Bee. “There were a whole lot of 'holy s***!' moments."

Authorities determined it would be best to arrest DeAngelo outside of his home and moved quickly to take him into custody.

DeAngelo was arrested outside his home Tuesday afternoon. He was booked into Sacramento County Jail on two charges of murder in the killings of Katie and Brian Maggiore, who were gunned down while walking their dog in Rancho Cordova in February 1978.

Investigators said they found a cache of firearms inside DeAngelo’s home.

"He is a very dangerous man, and he had an arsenal of guns at his home," Paul Holes, a newly retired investigator with the Contra Costa County Sheriff’s Office, told The Mercury News.

Holes, who officially retired three weeks before DeAngelo's arrest, had been on the Golden State Killer case for 24 years.

"This has always been my one big case that I was spending most of my time on," Holes said. "It was maybe a year ago when I realized that all the investigative strategies that I and others had employed just wasn’t cutting it, and trying to figure out how can we leverage the DNA technology."

Authorities announced DeAngelo’s arrest on National DNA Day, which Schubert called "fitting."

It was not immediately clear what DNA service lead police to suspect DeAngelo.

AncestryDNA, Vitagene, MyHeritage and 23andMe all have denied they provided any customer information to law enforcement officials.

The Golden State Killer is believed to have been responsible for at least 12 murders, 51 rapes and 120 home burglaries that occurred in at least 10 different counties in California in the 1970s and 80s.

At the start of his crime spree, testing to collect and identify DNA evidence had not yet been developed.

But in 2001, technology advances made it possible to prove the man dubbed the East Area Rapist was the same offender as the Original Night Stalker, now known as the Golden State Killer.

Crimes connected to who was then referred to as the Visalia Ransacker was also determined to be committed by the same person.

"The magnitude of this case demanded that it be solved,” Schubert told reporters on Wednesday. “The answer was and always was going to be, in the DNA."